Cationic lipids are amphiphilic molecules that generally contain a lipophilic region containing one or more hydrocarbon groups, and a hydrophilic region containing at least one positively charged polar head group. Cationic lipids are useful, because cationic lipids facilitate entry of macromolecules such as nucleic acids into the cytoplasm through the cell plasma membrane by forming a positively charged (total charge) complex with macromolecules such as nucleic acids. This process, performed in vitro and in vivo, is known as transfection.
Typically, cationic lipids are used either alone, or in combination with neutral lipids such as phospholipids. A combination of cationic lipids and neutral lipids is known to be useful, because it can easily form a vesicle that contains an aligned lipid bilayer. Vesicles and liposomes formed by cationic lipids either alone or in combination with neutral lipids have many positive charges on the surface, and, with these charges, can form a complex with polynucleotides or other anionic molecules such as negatively charged proteins. The remaining total cationic charge on the surface of a polynucleotide/cationic lipid/neutral lipid complex can cause strong interaction with the cell membrane, mainly with the negative charge on the surface of the cell membrane.
To date, many different cationic lipids have been synthesized for transfection, and are commercially available. Such cationic lipids include, for example, Lipofectin, Lipofectin ACE, Lipofect AMINE, Transfeactam, DOTAP, etc.
The N-[1-(2,3-dioleyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTMA), etc disclosed in Patent Document 1 are one of the cationic lipids developed in the early. DOTMA etc. are characterized by the propanaminium group having quaternary nitrogen providing a cationic part to the molecule, and a pair of higher hydrocarbons attached to the propyl backbone of the molecule by an ether bond. The quaternary nitrogen is trisubstituted with relatively short alkyl chains such as methyl groups. As structurally similar cationic lipid, N-(2,3-di-(9-(Z)-octadecenoyloxy))-prop-1-yl-N,N,N-trimethylammonium chloride (DOTAP) contains acyl groups, instead of the ether-bonded alkyl groups.
For example, the N-[1-(2,3-dioleyloxypropyl)]-N,N-dimethyl-N-hydroxyethylammonium bromide (DORIE), 2,3-dioleyloxy-N-[2-(spermine carboxamido)ethyl]-N,N-dimethyl-1-propanaminium trifluoroacetate (DOSPA), etc disclosed in Patent Documents 2 and 3 are characterized by the propanaminium group having quaternary nitrogen providing a cationic part to the molecule, and a pair of higher hydrocarbons attached to the propyl backbone of the molecule by an ether bond, the propanaminium group. The quaternary nitrogen is characterized by being trisubstituted with relatively short alkyl chains such as methyl groups, and with hydroxyalkyl.
Patent Document 4 discloses, for example, 1,2-dilinoleyloxy-N,N-dimethylaminopropane (DLinDMA), etc. DLinDMA, etc are characterized by the higher alkyl group that contains at least two unsaturated moieties. The higher alkyl group is contained as a replacement for the higher alkyl groups of the structurally similar cationic lipids DOTAP and DOTMA for the purpose of developing more flexible cationic lipids and improving the membrane fluidity of liposomes or the like. Patent Document 5 discloses, for example, 2,2-dilinoleyl-4-dimethylaminomethyl-[1,3]-dioxolan (DLin-K-DMA), etc.